TR1 provides a constant current to a bank of three zener diodes, thus maintaining a constant voltage independant of supply voltage variations. The resistor Rx is used to sense the PSU output current and to switches off the current to the zener diodes should the output current become excessive. The 1M0 (logarithmic taper) pot causes the current sensor (TR2) to `kick-in early`, so providing a variable current threshold limit. The value of RX should be (0.7/Amperes) ohms, where Amperes is the maximum output of the bench PSU. The prototype was set to 1-ampere, so Rx should be 0.5 / 1.000 = 0.5 ohms. The resistor should be rated at 1-watt, or 2x 1R0 500mW resistors in parallel for 1-ampere maximum output. I have used 4x 1R0 ohms in parallel (0.25 ohms) and have achieved 2-amperes (with a bigger heatsink).
Click here to download the full size of the above Circuit.
The reference diodes provide a voltage reference of 10.7-volts with tappings at 4.7-volts and 7.7-volts. The 7.7-volt tapping is used as the reference voltage. In this way we have a 6-volt swing selected by the 50K voltage pot, above and below the 7.7-volt reference. This voltage swing is amplified by the operational amplifer formed by TR3, TR4, TR5 and TR6. The DC output of the Op-Amp is arranged to give a voltage gain of a little over 2, so the 4.7-volts to 10.7-volts reference will become 0 to 15.4-volts at the output. I had thought about using PCB mounting pots, but the finished PCB is quite large and the heatsink must be quite substantial (see below). Here is the finished PSU PCB. I must emphasise that this is a prototype and not the final PCB which is much better in the layout. A full-wave rectifier provides the 18-volts input from a 15-0-15 volt mains input transformer. The diodes 1N5401 are rated at 3-amperes. At first sight, it would appear that 1-Ampere diodes, such as 1N4001, would suffice, but this is not the case. Althought the averge current through these diodes is alittle over 500mA, the 2700uf input capacitor will be charged with short pulses, each considerably higher than 500mA. If the 2700uf capacitor were to be increased in value, then the rectifier diodes may need to be rated even higher. I used two parallel 47000uf in the prototype PSU, mainly because I wanted more output current so an additional...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
characters left: